hash_func.c

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/*-
 * Copyright (c) 1990, 1993
 * The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Margo Seltzer.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 * This product includes software developed by the University of
 * California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)hash_func.c   8.2 (Berkeley) 2/21/94";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include "../include/db.h"
#include "hash.h"
#include "page.h"
#include "extern.h"

/* only one of these can be defined */
/* #define HASH1_EJB 1 */
/* #define HASH2_PHONG 1 */
/* #define HASH3_SDBM 1 */
#define HASH4_TOREK 1

static u_int32_t hashfunc __P((const void *, size_t));

/* Global default hash function */
u_int32_t (*__default_hash) __P((const void *, size_t)) = hashfunc;

/*
 * HASH FUNCTIONS
 *
 * Assume that we've already split the bucket to which this key hashes,
 * calculate that bucket, and check that in fact we did already split it.
 *
 * This came from ejb's hsearch.
 */

#ifdef HASH1_EJB

#define PRIME1    37
#define PRIME2    1048583

static u_int32_t
hashfunc(keyarg, len)
   const void *keyarg;
   register size_t len;
{
   register const u_char *key;
   register u_int32_t h;

   /* Convert string to integer */
   for (key = keyarg, h = 0; len--;)
      h = h * PRIME1 ^ (*key++ - ' ');
   h %= PRIME2;
   return (h);
}

#endif

#ifdef HASH2_PHONG
/*
 * Phong's linear congruential hash
 */
#define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))

static u_int32_t
hashfunc(keyarg, len)
   const void *keyarg;
   size_t len;
{
   register const u_char *e, *key;
   register u_int32_t h;
   register u_char c;

   key = keyarg;
   e = key + len;
   for (h = 0; key != e;) {
      c = *key++;
      if (!c && key > e)
         break;
      dcharhash(h, c);
   }
   return (h);
}
#endif

#ifdef HASH3_SDBM
/*
 * This is INCREDIBLY ugly, but fast.  We break the string up into 8 byte
 * units.  On the first time through the loop we get the "leftover bytes"
 * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle
 * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If
 * this routine is heavily used enough, it's worth the ugly coding.
 *
 * OZ's original sdbm hash
 */
static u_int32_t
hashfunc(keyarg, len)
   const void *keyarg;
   register size_t len;
{
   register const u_char *key;
   register size_t loop;
   register u_int32_t h;

#define HASHC   h = *key++ + 65599 * h

   h = 0;
   key = keyarg;
   if (len > 0) {
      loop = (len + 8 - 1) >> 3;

      switch (len & (8 - 1)) {
      case 0:
         do {
            HASHC;
            /* FALLTHROUGH */
      case 7:
            HASHC;
            /* FALLTHROUGH */
      case 6:
            HASHC;
            /* FALLTHROUGH */
      case 5:
            HASHC;
            /* FALLTHROUGH */
      case 4:
            HASHC;
            /* FALLTHROUGH */
      case 3:
            HASHC;
            /* FALLTHROUGH */
      case 2:
            HASHC;
            /* FALLTHROUGH */
      case 1:
            HASHC;
         } while (--loop);
      }
   }
   return (h);
}
#endif

#ifdef HASH4_TOREK
/* Hash function from Chris Torek. */
static u_int32_t
hashfunc(keyarg, len)
   const void *keyarg;
   register size_t len;
{
   register const u_char *key;
   register size_t loop;
   register u_int32_t h;

#define HASH4a   h = (h << 5) - h + *key++;
#define HASH4b   h = (h << 5) + h + *key++;
#define HASH4 HASH4b

   h = 0;
   key = keyarg;
   if (len > 0) {
      loop = (len + 8 - 1) >> 3;

      switch (len & (8 - 1)) {
      case 0:
         do {
            HASH4;
            /* FALLTHROUGH */
      case 7:
            HASH4;
            /* FALLTHROUGH */
      case 6:
            HASH4;
            /* FALLTHROUGH */
      case 5:
            HASH4;
            /* FALLTHROUGH */
      case 4:
            HASH4;
            /* FALLTHROUGH */
      case 3:
            HASH4;
            /* FALLTHROUGH */
      case 2:
            HASH4;
            /* FALLTHROUGH */
      case 1:
            HASH4;
         } while (--loop);
      }
   }
   return (h);
}
#endif